Non response makes it impossible to cancel

We signed up with ADT 8 months ago with the understanding that we'll be moving out of our current offices in the near future. However somewhere between their sales and our admin staff things got mixed up and we got signed up for a 24 month contract.<br> <br> Our contract states we can give written notice of 20 business days to cancel our contract at any time. We have send them 2 written notices of cancellation over the last 2 months and received no response. Calling the call center results in getting told we are on contract and can't cancel and if we insist they hang up or put you on hold indefinitely.<br> <br> Worst part is the building owner keeps tripping the alarm, which results in them phoning us or sending out a response car which we get billed for.